The disclosure herein builds on the content of the applicant's earlier UK patent application no. 0620060.4, filed on 10 Oct. 2006. That document describes a surgical cutting e.g. resection apparatus comprising a source of microwave radiation that is coupled to a surgical instrument having an antenna associated with a blade for cutting biological tissue, wherein the antenna is arranged to controllably deliver microwave energy from the source to a region where the blade cuts through tissue. The microwave energy can coagulate blood to effectively seal off the blood flow at the cutting region. Such an effect may be particularly beneficial when performing surgery on highly vascularised organs such as the liver or spleen.
The use of high microwave frequencies (e.g. 10 GHz or higher) offers particular advantage over the use of lower microwave frequency systems and RF systems due to the limited depth of penetration of the energy by radiation and the ability to enable small sharp blade structures to efficiently radiate energy into the tissue to seal off blood flow by being able to produce uniform fields along the length of the blade whilst at the same time being capable of cutting through the tissue to remove sections of diseased or cancerous tissue. The higher the microwave frequency, the more localised the energy distribution becomes and the energy density at the site where the cutting action takes place is correspondingly high, hence the easier it becomes to effectively seal off blood flow as the cutting blade is introduced into highly perfused biological tissue structures. The ability to localise the distribution of energy is advantageous in terms of limiting the amount of damage caused to healthy tissue. This feature may be particularly advantageous where it is required to remove large sections of diseased liver, where it is of paramount importance to save as much of the organ or healthy tissue as possible. A substantially uniform field profile can enable uniform coagulation or other tissue effects along the cutting edge. Using lower frequency microwave energy (e.g. 1 GHz or less) can lead to non-radiating regions of the antenna, which reduces the ability of the device to produce effective coagulation. By emitting a uniform field of microwave energy having a suitable energy density along the edge of the blade, the wound is effectively sealed as the surgeon cuts through the tissue structure.
In this specification microwave means the frequency range of between 2 GHz and 100 GHz, but preferably between 10 GHz and 25 GHz, and even more preferably between 14 GHz and 24 GHz. For example, spot frequencies of 14.5 GHz or 24 GHz may be used.
Higher frequencies (e.g. 24 GHz) may provide advantages such as a smaller size waveguide cable assembly, a smaller size antenna, i.e. the blade may be made to look similar in appearance and have the same physical dimensions as a standard scalpel blade, and smaller depth of penetration than lower frequencies (e.g. 14.5 GHz). For example, in liver at 24 GHz the depth of penetration is 1.1 mm, whereas it is 2 mm at 14.5 GHz. The smaller depth of penetration may permit higher energy density and more instant seal or coagulation to take place as the blade cuts into the tissue.
UK patent application no. 0620060.4 disclosed that a radiating section of the antenna may be dynamically tuned or impedance matched to a changing tissue load impedance (i.e. the distal tip of the radiating blade or structure may be adjusted to be the complex conjugate of the complex impedance of the treatment tissue) in order to optimise the level of power delivered into the tissue and to minimise reflected power. Additionally it was disclosed that the antenna may be arranged to enable measurements of tissue characteristics to be taken, e.g. using a treatment system as disclosed in WO 2004/047659 or WO 2005/115235.